Temperature response of bundle-sheath conductance in maize leaves

A small bundle-sheath conductance (g (bs)) is essential for the C(4) CO(2)-concentrating mechanism to suppress photorespiration effectively. To predict the productivity of C(4) crops accurately under global warming, it is necessary to examine whether and how g (bs) responds to temperature. We investigated the temperature response of g (bs) in maize by fitting a C(4) photosynthesis model to combined gas exchange and chlorophyll fluorescence measurements of irradiance and CO(2) response curves at 21% and 2% O(2) within the range of 13.5–39 °C. The analysis was based on reported kinetic constants of C(4) Rubisco and phosphoenolpyruvate carboxylase and temperature responses of C(3) mesophyll conductance (g (m)). The estimates of g (bs) varied greatly with leaf temperature. The temperature response of g (bs) was well described by the peaked Arrhenius equation, with the optimum temperature being ~34 °C. The assumed temperature responses of g (m) had only a slight impact on the temperature response of g (bs). In contrast, using extreme values of some enzyme kinetic constants changed the shape of the response, from the peaked optimum response to the non-peaked Arrhenius pattern. Further studies are needed to confirm such an Arrhenius response pattern from independent measurement techniques and to assess whether it is common across C(4) species.